大面源红外定标器热适配结构优化设计与验证

Optimal design and verification of thermal adaptive structure forinfrared calibrator with large surface

针对红外定标器在定标试验过程中因异质材料线膨胀系数不匹配导致结构热失配,造成低温状态下螺栓松动、降温速率慢、温度均匀性差,高温状态下玻璃钢隔热垫压溃等问题,开展大面源、宽温区、多材料体系红外定标器热适配结构优化设计与验证。从法向预紧力调控和面内翘曲变形控制两方面,筛选关键材料,调整装配参数,优化结构参数。采用仿真与试验相结合的手段,探究高低温状态下异质多层结构螺栓预紧力变化规律,验证红外定标器结构安全性和稳定性。最后通过升降温试验验证红外定标器关键技术指标。研究结果表明,选用聚四氟乙烯作为隔热材料,配合不锈钢螺栓,施加初始拧紧力矩介于10~18 N·m之间,调整安装孔孔径为25 mm以上,可有效控制预紧力变化,减小面内翘曲变形。全系统仿真结果表明在高低温状态下,连接安全有效的螺栓比例均达到了90%以上。热适配结构设计与优化可显著提高红外定标器降温速率,改善辐射面低温状态温度均匀性,结构安全性与稳定性满足设计要求。热适配结构优化设计方法可作为同类产品的参考。

Objective Infrared calibrators directly determine the detection accuracy of infrared devices as the reference standard for radiation measurement of infrared devices before the satellite launching.More precise infrared calibrators with large surface are required with the development of infrared optical satellites characterized by large aperture,large field of view and high precision,which means the structure of infrared calibrators must keep stable in high and low temperatures to guarantee the high temperature uniformity of the radiant surface,high precision of temperature control and high stability of the system.In the calibration test,the structure thermal mismatch easily occurs because the multilayered structure of infrared calibrators connected with bolts usually includes a variety of different materials and the deformations become unmatched during heating and cooling process for different thermal expansivity,which can reduce the calibration accuracy and increase security risks and test cost.As a result,optimal design and verification of thermal adaptive structure for the infrared calibrator with large surface,wide temperature range and multiple materials were carried out,to solve the problems caused by structure thermal mismatch,including the loose bolts,low cooling rate and bad thermal uniformity at the low temperatures,as well as the compression failure of heat insulating mattress made of glass reinforced plastic at the high temperatures.Methods From the two aspects of normal preload regulation and in-plane warping deformation control,the key materials were selected,the assembly parameters were adjusted and the structure parameters were optimized.Simulation analysis and tests were combined to explore the change rules of bolts preload on multilayered structure made of different materials when the temperature changed,at the same time verify the safety and stability of the structure.Finally,the key technical indexes of infrared calibrator were verified by means of heating and cooling tests.Results and Discussions The calculations based on the linear elastic theory indicated that the change of preload was controlled effectively by means of choosing Teflon as heat insulation material and stainless steel as bolt material(Tab.1),which provided a smaller relative deformation between bolts and connected members caused by the temperature change.The original preload was applied between 12 N·m to 20 N·m to avoid bolts looseness at−100℃ and deformation failure at 140℃(Tab.2).Furthermore,the diameters of mounting holes were enlarged to be greater than 25 mm to reduce the in-plane warping deformation resulting from bolts shearing(Tab.3).The tightening torque test based on multilayered structure composed of different materials discovered the rules that the tightening torque got linear relation with the deformation in the certain range. The elastic deformation occurred atthe low temperatures and on the other hand the plastic deformation was more likely to occur at the hightemperatures. The axial stiffness of multilayered structure could be improved by repeating heating and coolingprocess (Fig.4). The simulation result of the whole system suggested that the proportion of bolts with safe andeffective connections had reached more than 90% under the high and low temperatures (Tab.3). The stress of boltsat the upper and lower edges of the calibrator changed more significantly than that at other positions and thereforedifferent assembly parameters could be set according to the bolt positions. The heating and cooling test of infraredcalibrator showed that the structure was safe and stable with the temperature change, the cooling time wasshortened from 30 h to 4 h (Fig.7), and the temperature deviation of the radiant surface at 193 K was improvedfrom −0.8 K/+0.9 K to −0.3 K/+0.4 K.Conclusions The optimal design of thermal adaptive structure can significantly increase the cooling rate ofinfrared calibrator and improve the thermal uniformity of radiant surface at the low temperatures. The difficultiesof loose bolts at the low temperatures and compression failure of heat insulating mattress at the high temperatureswere overcome at the same time. This study solved the practical problems in the calibration test and the structuralsafety and stability after optimal design can meet the design requirements. The optimal design methods of thermaladaptive structure can be referred for the same type of products.